The subject matter disclosed herein generally relates to propulsion systems for aircraft use. More specifically, the subject disclosure relates to cooling of gearbox components for propulsor systems of rotary wing aircraft.
A rotary wing aircraft with a coaxial contra-rotating rotor system is capable of higher speeds as compared to conventional single rotor helicopters due in part to the balance of lift between advancing sides of the main rotor blades on the upper and lower rotor systems. To still further increase airspeed, supplemental translational thrust is provided by a translational thrust system including an integrated propulsor unit with a propulsor (e.g., a propeller) oriented substantially horizontal and parallel to the aircraft longitudinal axis to provide thrust for high speed flight. Such a rotary wing aircraft may be referred to as a hybrid helicopter.
In such hybrid helicopters, the propulsor is driven by a propulsor shaft coupled to the helicopter engine along with the coaxial contra-rotating rotor system. The shaft output speed of the engine is particularly high, to enable high speed rotation of the rotor system, while such high rotational speed is often not necessary or desired for the propulsor, so the propulsor is coupled to the propulsor shaft via propulsor gearbox for reduction of propulsor rotational speed. The propulsor gearbox in turn requires cooling for its lubrication system, and this cooling system should be drag efficient for the aircraft, by not significantly increasing the cross-sectional area while meeting cooling performance requirements.